This invention relates to a gear train structure for a timepiece and, in particular, to improvements in a slip mechanism for use in the gear train.
In conventional slip mechanisms, it has heretofore been practiced generally, for example, to combine a pinion with a gear placed on it and a spring mounted further thereon by way of calking thereby intensely urging the gear to the pinion by the spring to connect them frictionally.
Such method is, however, disadvantageous from an economical point of view since connecting steps such as calking are required and a great loss result for each faulty or defective assembly produced.
Another conventional method has been known in which a gear is fabricated from metal and integrally formed together with a pinion upon plastic molding of the latter.
This method is also defective in that the slip torque is greatly changed with even a slight variation in forming conditions because the slip torque is determined by the force resulted between the metal and the plastic upon forming of the assembly.
A further method of providing a flexible arm to either one of a gear and a pinion made of plastic to obtain a slip torque by frictionally connecting them with the flexible arm is defective in that a reliability of the slip mechanism is very low since the slip torque tends to change with even slight changes in temperature and humidity.
It is, accordingly, an object of this invention to eliminate the foregoing drawbacks and provide a structure which is inexpensive and quickly and easily highly reliable and capable of connection with a gear train assembly.
The foregoing defects can be overcome by a slip mechanism comprised of a gear, pinion and a spring, in which the pinion is formed with a guide portion for rotationally guiding the gear, a supporting portion for bearing the height of the spring and an anti-rotation portion for the spring, and designed such that the pinion and the spring are rotated together upon slipping.